1. Field of the Invention
The present invention relates to a solid-state imaging device, and more particularly, to a solid-state imaging device for use in a digital still camera, a digital video camera, and the like.
2. Description of the Related Art
In a digital still camera or a video camera, technologies for detecting distances for auto focusing (AF) are known. With regard to such technologies for detecting distances for AF, Japanese Patent No. 3592147 proposes a solid-state imaging device in which a part of pixels of an imaging device have a ranging function and the detection is made by a phase difference system.
The phase difference system is a method in which optical images which pass through different regions on a pupil of a camera lens are compared and triangulation using a stereo image is used to detect the distance.
In such a method, differently from the case of a conventional contrast system, it is not necessary to move the lens in order to carry out ranging, and thus, AF at high speed with high precision is possible. Further, real-time AF when moving images are taken is possible.
In the above-mentioned Japanese Patent No. 3592147, a ranging pixel has between a microlens and a photoelectric conversion unit an opening which is off center with respect to an optical center of the microlens.
This enables selective introduction of light which passes through a predetermined region on the pupil of the camera lens to the photoelectric conversion unit to carry out ranging.
However, in the structure described in Japanese Patent No. 3592147 having the off-center opening, due to light scattering at a wiring member or the like, there is a possibility that light flux can not be separated enough and the ranging precision is lowered.
Further, when the structure described in Japanese Patent No. 3592147 is applied to a solid-state imaging device with a small pixel size, there is a possibility that the following problem arises.
As the pixel size becomes smaller, the F value of the microlens for introducing light to the photoelectric conversion unit becomes larger, and the pixel size and the size of a diffraction image become almost the same.
Therefore, light diverges in the pixel, and thus, there is a possibility that light flux can not be separated enough at the off-center opening and the ranging precision is further lowered.